Electrostatic levitation furnance

ABSTRACT

An electrostatic levitation furnace is improved by providing three pairs of electrodes opposed to each other respectively on three axes perpendicularly intercepting each other at a position where the sample is to be levitated in the vacuum chamber, and disposing a plurality of access ports, which are directed to the position of the sample, to the vacuum chamber tree-dimensionally, whereby the accessible direction against the sample is diversified, it becomes possible to improve the degree of freedom in distribution of various apparatuses and easily cope with increase of apparatuses.

TECHNICAL FIELD

This invention relates to an electrostatic levitation furnace, which isused for suspending a charged sample in a levitation state in anelectrostatic field generated between electrodes and subjecting thesample to heating process.

BACKGROUND ART

There is an electrostatic levitation furnace as a conventionallevitation furnace, which is provided with a flat and nearly cylindricalshaped vacuum chamber, a pair of main electrodes disposed on Z-axis thatis an axis of this vacuum chamber, a pair of auxiliary electrodesrespectively disposed on X-axis and Y-axis intersecting perpendicularlyto the Z-axis, and a plurality of access ports disposedtwo-dimensionally in a periphery of the vacuum chamber at predeterminedspaces. The respective access ports are equipped with variousapparatuses, such as a laser irradiator for heating the sample, aposition detector for the sample, a thermal measuring device for thesample, an illuminator, a camera and so on.

In the electrostatic levitation furnace described above, the samplecharged between main electrodes is charged by electrode contact,ultraviolet irradiation or heating, and made in the levitation state bythe electrostatic field generated between main electrodes. In this time,the sample is held in the predetermined position by controlling electricpotential between main electrodes and between auxiliary electrodes, andthe sample is heated and molten by irradiating laser beams thereon. Itis possible to generate a crystal without external interference bycooling and solidifying the sample heated and molten in this manner.

Additionally, although there is a furnace designed so as to levitate thesample by using an acoustic wave or an electromagnetic method as thefurnace for making the sample in the levitation state, it is necessaryto introduce a gaseous body into the furnace in a case of using theacoustic wave, so that the sample may be influenced by the gaseous body,and the sample is confined to a conductive body in a case of using theelectromagnetic method. As compared with above, the electrostaticlevitation furnace has the advantage in that the furnace can be appliedalso to the sample other than the magnetic body without the influence ofthe gaseous body because of making the inside of the furnace vacuous.

However, in the aforementioned conventional electrostatic levitationfurnace, the main electrodes is disposed on the axis of the vacuumchamber and the access ports is disposed two-dimensionally along theouter periphery of the vacuum chamber, therefore there are problems asfollow.

{circle over (1)} It is difficult to increase the number of theapparatuses for access and distribute these apparatuses since theaccessible direction against the sample is substantially limited withinonly one plane and the auxiliary electrodes are also disposed on thisplane.

{circle over (2)} The auxiliary electrodes of which electrostatic fieldintensity is low as compared with the main electrodes cannot but be usedfor reasons of distributing the various apparatuses, so that controllingforces in the directions of X and Y-axes becomes weak.

{circle over (3)} If the access ports are increased in number accordingto demand of access against the sample, the outer diameter of the vacuumchamber becomes larger and the equipment becomes larger in the wholebody because the vacuum system becomes necessary to increase thecapacity following this. In a case of scaling up of the equipment in thewhole body as mentioned above, the distance from the sample becomeslonger, so that the access against the sample becomes difficult,furthermore it becomes improper to be used in the spacecraft in whichthere is a severe limitation in size and weight.

{circle over (4)} It is difficult to heat the sample uniformly becausethe irradiating direction of laser beams is also restricted within oneplane.

Further, there is also a problem in that the respective electrodes arefixed to the vacuum chamber in the conventional electrostatic levitationfurnace and it is not possible to change the space between theelectrodes and the size of the electrodes according to size of thesample or so.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the aforementionedproblem in the conventional arts, and it is an object to provide anelectrostatic levitation furnace, which is possible to increase theaccessible direction to the sample, thereby enabling realization ofextension of the various apparatuses and improvement of heatingfunctions for the sample in spite of the body small in size.

The electrostatic levitation furnace according to this invention is afurnace for generating electrostatic field between electrodes disposedin a vacuum chamber and making a charged sample into a levitation statein the electrostatic field between the electrodes, and characterized bycomprising three pairs of electrodes opposed to each other respectivelyon three axes perpendicularly intercepting each other at a positionwhere the sample is to be levitated in the vacuum chamber and aplurality of access ports disposed tree-dimensionally to the vacuumchamber and directed to the position of the levitating sample.

In the aforementioned electrostatic levitation furnace, three pairs ofelectrodes are provided in the vacuum chamber, and each of pairs ofelectrodes are opposed to each other on one of three axesperpendicularly intercepting each other. The sample is made into thelevitation state by the electrostatic field generated between theseelectrodes and maintained in the predetermined position by controllingelectric potential between the respective electrodes. Further, theaccess ports directed to the position of the sample aretree-dimensionally disposed to the vacuum chamber, and these accessports are provided with various apparatus, such as a laser irradiatorfor heating the sample, a position detector for the sample, a thermalmeasuring device for the sample, an illuminator, a camera and the like.The accessible direction to the sample becomes multiple differing fromthe conventional furnace by disposing the access portstree-dimensionally as mentioned above, whereby it becomes easy to avoidinterference between the apparatuses and the electrodes, the degree offreedom in distribution of the apparatuses is increased and theextension of the apparatuses becomes easier to be dealt with.

The electrostatic levitation furnace according to this invention is alsocharacterized by making the three pairs of electrodes equivalent intheir electrostatic field intensity.

In the furnace as mentioned above, three pairs of electrodes generateelectrostatic fields equivalent in their intensity. Namely, theelectrodes can be disposed without severe restriction owing to thedistribution of various apparatuses when the accessible directionagainst the sample becomes more multiple, so that tree pair of theelectrodes equivalent in electrostatic field intensity become possibleto be introduced. Whereby, controlling forces in the directions of threeaxes caused by the respective electrodes becomes uniform and the sampleis securely maintained at the predetermined position in the levitationstate.

The electrostatic levitation furnace according to this invention isfurther characterized by disposing a detachable cage in the vacuumchamber and providing the respective electrodes to this cage.

In the above-mentioned electrostatic levitation furnace, the cageprovided with the electrodes are attached to the vacuum chamber,therefore the respective electrodes may be disposed in the predeterminedpositions in the vacuum chamber. Furthermore, since the cage isdetachable from the vacuum chamber, it is possible to selectively usethe plural cages according to size of the sample or so, by preparing theplural cages provided with the electrodes differing in size and (or)space between the opposite electrodes in advance.

Further, the electrostatic levitation furnace according to thisinvention is characterized by providing the respective electrodesdetachably from the cage.

In the aforementioned electrostatic levitation furnace, it is possibleto selectively attach the electrodes differing in size and (or) spacebetween the opposite electrodes against the common cage because therespective electrodes are detachably from the cage.

Furthermore, the electrostatic levitation furnace according to thisinvention is characterized by providing power terminals to the cage.

In the aforementioned electrostatic levitation furnace, the cage may beattached with the electrodes or the apparatuses required for powersupply since the cage is provided with the power terminals.

The electrostatic levitation furnace according to this invention isfurther characterized by providing the laser irradiators for irradiatinglaser beams against the sample at respective points corresponding toapexes of a triangular pyramid having the center coincides with theposition where the sample is to be levitated.

In the aforementioned furnace, it becomes possible to arrange the laserirradiators as described above, because the accessible direction to thesample becomes multiple. So that, the sample is heated uniformly byirradiating laser beams to the sample from the four laser irradiatorssituated at the respective apexes of the triangular pyramid.

The electrostatic levitation furnace according to this invention is alsocharacterized by providing the laser irradiator for irradiating laserbeams against the sample at one of respective electrodes.

In the furnace as mentioned above, the laser irradiator is provided toone of electrodes, for example, to the upper electrode on the verticalaxis in a case of subjecting the sample to the heating process in thegravitational field. The sample is heated and charged by irradiatinglaser beams from the laser irradiator, and successively levitatedaccording to the electrostatic field generated between the electrodes.

The electrostatic levitation furnace according to this invention isfurther characterized by providing a chuck for holding the sample to bereleased between the electrodes, and the chuck is provided with a pairof holder pieces energized in the closing direction for pinching thesample therebetween.

In the furnace as mentioned above, the sample is held with the chuckbeforehand, and is made to be released from the chuck as the positivelycharged sample moves toward the negative electrode, especially inapplication in the zero-gravity space (including micro-gravity space).In a case of, for example, using a chuck of opening type, the contactbetween the sample and the chuck on the whole is not always uniform,therefore there is high possibility of providing rotation to thereleased sample according to uneven contact of the sample with theopening chuck. If the sample is rotated, it becomes impossible to obtainuniform composition owing to centrifugal force caused by the rotation.Therefore, in this electrostatic levitation furnace, the sample is keptto be held between pair of holder pieces of the chuck energized in theclosing direction and the pair of holder pieces is closed with themovement of the charged sample. The sample is released between theelectrodes without rotation by activating the pair of holder pieces inthe closing direction as mentioned above.

Furthermore, the electrostatic levitation furnace according to thisinvention is characterized by disposing the laser irradiator to theelectrode on the lower side between vertically opposed electrodes in thegravitational field.

In the aforementioned electrostatic levitation furnace, which isprovided with the electrodes opposed in the vertical direction in thegravitational field, laser beams are irradiated to the sample from thelaser irradiator disposed to the lower electrode. Concretely, in a casewhere the principal element of the sample is high-melting point metalfor example, the sample is heated up to a temperature lower than themelting point (1200° C. or so, for example) by irradiating laser beamsto the sample from the lower side, thereby removing low-melting elementscontained in the sample and electrifying the sample. After this, thesample is made into the levitation state between electrodes as it is orafter cooling, and then the sample is heated into melting state byirradiating laser beams. In such the case of making the sample into thelevitation state by irradiating laser beams from under side of thesample, pressure of laser acts in the direction in which the gravity iscancelled, and the charged state of the sample is maintainedefficiently.

The electrostatic levitation furnace according to this invention is alsocharacterized by forming the top end face of the lower electrode in ahemi-spherically concave shape.

In the aforementioned furnace having the lower electrode with ahemi-spherically concave face on the top end, radiant heat istransferred efficiently toward the sample by the top end face (concaveshape) of the electrode at the time of heating the sample with laserbeams.

Moreover, the electrostatic levitation furnace according to thisinvention is characterized by providing a net-like shaped holding meansfor placing the sample to the lower electrode.

In the aforementioned furnace of which electrode on the lower side isequipped with the net-like shaped holding means for placing the sample,a net made of, for example, tungsten is applied as the holding means. Inthis electrostatic levitation furnace, the electrode face is preventedfrom damage in the high-temperature environment by heating the sampleplaced on the holding means with laser beams.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view explaining an example of the electrostaticlevitation furnace according to this invention;

FIGS. 2(a) and (b) are side views of the electrostatic levitationfurnace shown in FIG. 1 differing in the observation angle from eachother;

FIG. 3 is a sectional view illustrating assembling procedure of the cageagainst the vacuum chamber;

FIG. 4(a) is a sectional view of the cage at the position of the samplesupplier;

FIG. 4(b) is a sectional view of the necessitated portion illustrating astate of supplying the sample;

FIG. 5 is a sectional view of the cage illustrating a laser beam path onthe Z-axis;

FIGS. 6(a) and (b) are sectional views explaining a process forcollecting the sample;

FIG. 7 is a schematic explanatory view showing the sample maintained inthe levitation state;

FIG. 8 is a schematic explanatory view showing distribution of the laserirradiators against the sample;

FIGS. 9(a)˜(e) are sectional views explaining a process for releasingthe sample;

FIGS. 10(a)˜(d) are sectional views explaining a process for collectingthe sample;

FIG. 11 is a sectional view of the necessitated portion explaininganother example of the electrostatic levitation furnace according tothis invention;

FIGS. 12(a) and (b) are a plan view and a sectional view showing a stateof placing the sample on the holding means of the positive electrodeshown in FIG. 11, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

An example of the electrostatic levitation furnace according to thisinvention will be described below on basis of the drawings. Theelectrostatic levitation furnace according to this invention is ofcourse not limited only to the example as described blow in the detailsof construction of the respective parts.

An electrostatic levitation furnace 1 shown in FIGS. 1 to 3 is providedwith a vacuum chamber 3 forming a space 2 having nearly cylindricalshape opened in the vertical direction, a cover plate 4 for blocking theupper side of the vacuum chamber 3 in airtight, an electrode-base fixingpedestal 5 having a pipe-like shape and inset coaxially from lower sideof the vacuum chamber 3, and a fitting flange 6 fixed to the undersideof the vacuum chamber 3 in airtight, and this furnace 1 is secured to abase plate 51 shown with two-dot chain lines through the fitting flange6.

The vacuum chamber 3 has an octagonal section and a sidewall dividedinto three parts in the vertical direction, therefore the vacuum chamber3 is formed with 24 faces on the sidewall, and access ports P aredisposed on the respective faces of the sidewall. Further, the coverplate 4 is equipped with a cage 7 disposed with openings in accordancewith the distribution of the respective access ports P.

The cage 7 is detachable together with the cover plate 4 against thevacuum chamber 3, and maintained inside of the respective access ports Pin the space 2 in the state of fixing the cover plate 4 to the vacuumchamber 3. In this state, the center of the cage 7 agree with a positionin which a sample A is to be levitated, and the respective access portsP are directed to the position of the levitating sample A and disposedin tree-dimensional.

The electrode-base fixing pedestal 5 is provided with a filter 8 atouter periphery of the top end protruding into the space 2, and thespace 2 communicates with outside of the vacuum chamber 3 through thefilter 8. The fitting flange 6 is equipped with a pipe 11 including aconnecting portion 9 to a vacuum pump and a connecting portion 10 to aninactive gas source. The pipe 11 is situated coaxially with theelectrode-base fixing pedestal 5 and communicates with the space 2through the inside of the electrode-base fixing pedestal 5.

The cage 7 is provided with a plug 12 and detachable from a socket 13secured to the under face of the cover plate 4. The plug 12 and thesocket 13 form a well-known connector used for the fluid coupling or so.

Namely, the socket 13 is formed in a cylindrical shape and provided withthe proper number of engaging balls 14 freely going in and out insidethereof, and a sleeve 16 fitted thereon and energized downwardly by aspring 15. On the other side, the plug 12 is formed with a depression 17corresponding to the engaging balls 14 on the outer periphery thereof.The plug 12 and the socket 13 are designed so as to keep the connectedstate by inserting the plug 12 inside of the socket 13 as shown in FIG.1, engaging the balls 14 projecting inside of the socket 13 into thedepression 17 of the plug 12 and restricting the engaging balls 14 inthe projecting state with the sleeve 16. In this time, the restrictionof the engaging balls 14 is cancelled by moving the sleeve 16 upwardlyagainst elasticity of the spring 15, and the plug 12 can be disengagedfrom the socket 13.

The cage 7 is disposed with three pair of electrodes opposed to eachother respectively on three axes perpendicularly intercepting each otherat the position where the sample A is kept in the levitation state asshown also in FIG. 4 and FIG. 5. In this example, the upper electrode isdenoted as a negative electrode EZ1 and the lower electrode is denotedas a positive electrode EZ2 on vertical Z-axis. Electrodes of one sideare denoted as negative electrodes EX1 and EY1 and the other electrodesare denoted as positive electrodes EX2 and EY2 on horizontal X andY-axes, respectively. All of three pairs of electrodes are equivalent intheir electric intensity and detachable from the cage 7 at will.

The negative electrode EZ1 on the Z-axis is fitted to an insulatingholder 18 screwed to the cage 7, and connected with the power source viaa path passing through the cover plate 4. Further, the negativeelectrode EZ1 is provided with an opening 19 that works as a laserirradiator at the center thereof. Correspondingly, a reflector 20 and acondenser lens 21 forming an optical path are housed in the insulatingholder 18, and the cage 7 is attached with another reflector 22similarly forming the optical path.

As shown in FIG. 5, laser beams L passed through the access port P arereflected by both the reflectors 22 and 20 and irradiated to the sampleA through the opening 19 of the negative electrode EZ1 after beingcollected by the condenser lens 21. In this example, laser beams Lirradiated from the opening 19 are used for heating and electrifying,whereby the sample A is heated and charged.

The positive electrode EZ2 on the Z-axis is similarly fitted to aninsulating holder 23. The insulating holder 23 is screwed against aninsulating base 24 fixed to the cage 7 with bolts. The positiveelectrode EZ2 has the upper face formed in a concave shape and isprovided with an aperture 25 at the center of the concave face forpassing the sample A. Correspondingly, the insulating holder 23 servesalso as a collecting receptacle and is provided with a ceramic shutter26 held at the upper limit by a spring, a solenoid 27 forming anelectromagnet for moving the shutter 26 to the lower limit and a controlpin 28 inserted on the axis of the shutter 26.

The shutter 26 forms a ring-shaped housing space 29 together with theinsulating holder 23, and is so designed as to block the aperture 25 ofthe positive electrode EZ2 with the upper end thereof at the time oflocating in the upper limit. The control pin 28 is secured to theinsulating holder 23, the top end formed with a slope 28 a of thecontrol pin 28 is situated on a lower side of the aperture 25 and formedso as to protrude from the upper end of the shutter 26 when the shutter26 moves to the lower limit. The solenoid 27 is connected with powerterminals 30 provided to the cage 7. The power terminals 30 connected tothe power source via the path passing through the cover plate 4similarly to the aforementioned negative electrode EZ1. The collectingoperation of the sample A will be described later.

The above-mentioned positive electrode EZ2 is connected with aconductive part 31 provided to the center of the under face of theinsulating base 24. Additionally, the insulating base 24 is formed withirregularities by using suitable ribs on the outer surface thereof andthe insulation performance is further improved by increasing exteriordistance from the conductive part 31 with high voltage to the cage 7with zero-potential because a high-tension electric power is used inthis electrostatic levitation furnace 1. Furthermore, all of therespective electrodes EX1, EX2, EY1 and EY2 on the X and Y-axes arefitted to insulating holders 32 screwed to the cage 7 and provides withconductive parts 33 exposed at base ends of the insulating holders 32,respectively.

Moreover, the cage 7 is fitted with a sample supplier 34 for supplyingthe sample A to the upper face of the positive electrode EZ2 on theZ-axis. The sample supplier 34 is provided with an outer cylinder 35secured to the cage 7, an inner cylinder 36 inserted in the outercylinder 35 and an injection pin 37 inserted in the inner cylinder 36,and a plurality of the spherical sample A is contained in the innercylinder 36. The inner cylinder 36 is held at the receding position by afirst spring S1 intervening between the outer cylinder 35 and the innercylinder 36, and the injection pin 37 is similarly held at the recedingposition by a second spring S2 intervening between the inner cylinder 36and the injection pin 37.

In this time, the second spring S2 has larger spring constant ascompared with the first spring S2. Further, the outer cylinder 35 isequipped with a cover 50 for covering and uncovering the top end of theinner cylinders 36. The cover 50 has elasticity enough to carry out thecovering and uncovering action and is formed with heat-resisting resin.The outer cylinder 35, the inner cylinder 36, the first and secondsprings S1 and S2, and the injection pin 37 are assembled in a coaxialstate so as to be smoothly actuated in the axial direction by amanipulator as described later. The supplying operation of the sample Awill be described later.

The positive electrode EZ2 on the Z-axis, the respective electrodes EX1,EX2, EY1, EY2 on the X and Y-axes and the sample supplier 34 asdescribed above are attached with an electrode base and the manipulatoron the side of vacuum chamber 3.

The aforementioned electrode-base fixing pedestal 5 is fixed with anelectrode base 38, which is provided with a power-leading terminal 39corresponding to the conductive part 31 of the insulating base 24.Furthermore, ports corresponding to the respective electrodes EX1, EX2,EY1, EY2 on the X and Y-axes among the aforementioned access ports P arefixed with electrode bases 40 respectively, and the respective electrodebases 40 are attached with power-leading terminals 41 corresponding tothe conductive parts 33 of the respective electrodes EX1, EX2, EY1 andEY2 in a state of being elastically held so as to protrude the top endsof them. These power-leading terminals 39 and 41 are connected to thepower source on the outside of the drawings.

Furthermore, a port corresponding to the sample supplier 34 among therespective access ports P is installed with a manipulator 42. Themanipulator 42 is provided with a fixing member 43, an operational rod44 inserted slidably into the fixing member 43 and an operating knob 45for moving the operational rod 44 in the axial direction, and theoperational rod 44 is attached with a pusher rod 47 elastically held bya guide pin 46A and a spring 46B coaxially in the axial direction.

When the above-mentioned electrode bases 38, 40 and the manipulator 42are fitted to the vacuum chamber 3 together with the cover plate 4, theconductive parts 31 and 33 of the respective electrodes EZ2, EX1, EX2,EY1 and EY2 come in contact with the power-leading terminals 39 and 41respectively, whereby the respective electrodes EZ2, EX1, EX2, EY1 andEY2 are made into states connected with the power source, and theinjection pin 37 of the sample supplier 34 and the pusher rod 47 of themanipulator 42 come to coincide on the same axis line. Namely, therespective apparatus on the inside and outside of the vacuum chamber 3are made into operable interlocking states by merely fitting the cage 7to the vacuum chamber 3.

Moreover, the access ports P are disposed with the laser irradiator forheating the sample A, and various apparatuses in addition to this, suchas a position detector for the sample A, a thermal measuring device forthe sample A, an illuminator and a camera. The access ports P disposedwith these apparatuses are blocked up by windowpanes, and windows may beinstalled to some of access ports P for observing inside of the vacuumchamber 3.

In this electrostatic levitation furnace 1, laser irradiators Q1 to Q4are disposed at the points corresponding to the respective apexes of atriangular pyramid (shown with two-dot chain lines) having the center atthe position where the sample A is to be levitated as shown in FIG. 8,for example. The access ports P opposed to the laser irradiators Q1 toQ4 among the aforementioned access ports P are provided with laserdumpers 48 for receiving laser beams deviating from the sample A, andthe laser dumpers 48 are covered with safety covers 52 made of punchingmetal plates as shown in FIG. 1.

In this case, although the laser dumper is not equipped against laserbeams irradiated from the opening 19 of the negative electrode EZ1 onthe Z-axis since the positive electrode EZ2 is existing on the Z-axis,the laser emitter is controlled on basis of input signals from the aposition detector for the sample A so as to discontinue the laseroscillation in a case where laser beams are likely to deviate from thesample A.

The electrostatic levitation furnace 1 is formed with a cooling jacketat proper parts of the vacuum chamber 3 for performing the heatingprocess of the sample A, whereby a cooling fluid is circulated throughcooling pipes 49 connected with this cooing jacket.

Next, an operation of the electrostatic levitation furnace 1 having theaforementioned construction will be explained below, concerning a caseof subjecting the sample to heating process under the gravitationalfield.

First of all, the vacuum chamber 3 is evacuated to make the space 2vacuous after setting the case 7 to the vacuum chamber 3 together withthe cover plate 4 as shown in FIG. 1. Next, the sample A is cast to thepositive electrode EZ2 by the manipulator 42. Namely, the operationalrod 44 goes forward by operating the operation knob 45 of the maniulator42, thereby pushing the injection pin 37 of the sample supplier 34 withthe pusher rod 47 at the top end thereof. In this time, the innercylinder 36 goes forward together with the injection pin 37 at the sametime of compressing the first spring S1 in advance because the springconstant of the second spring S2 is larger than that of the first springS1, the inner cylinder 36 thrust the cover 50 aside and further goesforward, consequently the uncovered top end of the inner cylinder 36arrives by the side of the positive electrode EZ2 as shown in FIG. 4(b).

By making the operational rod 44 to go forward successively, theinjection pin 37 goes forward at the same time of compressing the secondspring S2, thereby releasing the sample A on the upper face of thepositive electrode EZ2. The sample A to be released is a single one inthis time. The released sample A is located at the upper end of theshutter 26 after rolling to the center as shown in FIG. 6(a), since theupper face of the positive electrode EZ2 is formed in the concave shape.After this, the sample supplier 43 is made a backward movement.

Subsequently, heating electrification is made for the sample A byirradiating laser beams toward the sample A from the opening 19 of thenegative electrode EZ1 on the Z-axis. The sample A is levitated towardthe negative electrode EZ1 on the upper side by electrifying the sampleA positive in this manner. Although the heating electrification iscarried out in this example, it is also possible to perform contactelectrification through the positive electrode EZ2 by making the upperend part of the ceramic shutter 26 with a metal and forming an electricconductive path to the sample A from the positive electrode EZ2 on theZ-axis.

Thereafter, the sample A is held floatingly at a certain height by theelectrostatic field generated with the electrodes EZ1 and EZ2 on theZ-axis, and further held floatingly on the Z-axis by controlling theelectrostatic field generated between the electrodes EX1 and EX2, EY1and EY2 on the X and Y-axes as to the horizontal direction. For example,if the sample A deviates in the direction of X-axis as shown in FIG. 7,the sample A is returned onto the Z-axis by generating electrostaticfield in the direction of X-axis and making electric potential zero inthe direction of Y-axis.

In the state of holding the sample A at the center of the cage 7 asdescribed above, the sample A is heated and molten by irradiating laserbeams toward the sample A from the laser irradiators Q1 to Q4 disposedat the four places as shown in FIG. 8. In this time, the sample A can beheated uniformly because the laser irradiators Q1 to Q4 disposed at theplaces corresponding to the respective apexes of the triangular pyramidin this electrostatic levitation furnace 1. In the case of heating, itis also possible to irradiate laser beams for the electrificationheating in addition to the laser beams from the four places. After that,the molten sample A is cooled and solidified while it is left in thelevitation state. In such the manner, crystallization is performed inthe sample A in a state of perfectly eliminating external interferencein this electrostatic levitation furnace 1.

After completing the heating process for the sample A, the aperture 25is opened by moving the shutter 26 to the lower limit through thesolenoid 27, and then the sample A is made to fall by making theelectric potential between the electrodes into zero. In this time, sincethe control pin 28 sticks out from the upper end of the shutter 26 andformed with the slope 28 a at the top end thereof as shown in FIG. 6(b),the sample A is securely guided into one side by the slope 28 a afterpassing through the aperture 25 and falls into the housing space 29.After that, the shutter 26 returns to the upper limit by interruptingcurrent supply to the solenoid 27, and the collection of the sample A iscompleted. The sample A is certainly collected in the housing space 29by dropping the sample A after opening the aperture 25 in this manner.

In the electrostatic levitation furnace 1, the plural number of thesamples A are collected in the insulating holder 23 by repeating theaforementioned operation. This insulating holder 23 is used as a samplecase in itself by removing it from the cage 7.

As mentioned above, in the electrostatic levitation furnace 1 of thisexample, the accessible direction against the sample A is multiple, suchas the heating of the sample, the position detection, the temperaturemeasurement, the illumination, the photographing and so on, in additionto the generation of the electrostatic field against the sample A fromthree directions, therefore it is possible to easily avoid theinterference between the electrodes EZ1, EZ2, EX1, EX2, EY1, EY2 and thelaser irradiators Q1 to Q4 or the other apparatuses, the degree offreedom is very high in distribution of the apparatuses in spite of thesmall-sized body and it is easy to deal with the increase of theapparatuses as compared with the case of accessing the sample on thesame plane as described concerning the conventional electrostaticlevitation furnace.

Further, it is possible to obtain the sufficient vacuum atmosphere evenby the small-sized vacuum system according to miniaturization of thevacuum chamber 3, and it is easy to introduce, for example, themanipulator 42 because of short distance from the sample A.

Furthermore, the cage 7 is detachable from the inside of the vacuumchamber 3, the electrodes EZ1, EZ2, EX1, EX2, EY1and EY2 are detachablefrom the cage 7, and the power terminals 30 are provided to the cage 7,therefore it is possible to change the space and the size of theelectrodes in accordance with the size of the sample A or so, and thecage 7 can be disposed with the apparatuses required to be connectedwith the power source such as solenoid 27 for actuating the opticalinstruments such as the reflectors 20 and 22, the condenser lens 21 orso and the shutter 26, thereby simplifying the setting work of theseapparatuses.

Especially, the cage 7 can be attached with condenser lenses 53(partially shown in FIG. 1) for collecting laser beams L from the laserirradiators Q1 to Q4, and such the structure becomes very effective inorder to irradiate laser beams. Namely, semiconductor laser is used forexample in this electrostatic levitation furnace 1, laser beams from thelaser emitter is conducted through an optical fiber tube and irradiatedto the sample. In this case, laser beams radiated from the optical fibertube has a tendency to diffuse. In a case of assumingly trying toirradiate such the laser beams to the sample A after collecting on theoutside of the vacuum chamber 3, it is difficult to adjust the focus inaccurate because of long distance from the sample A and the diameter ofthe spot becomes larger. Further, the laser beams pass the access port Pin a concentrated state, accordingly the windowpane of the port P isrequired to be applied with a heat-resisting coating or the like.

As compared with the above, in this electrostatic levitation furnace 1,which is disposed with the condenser lenses 53 in the vicinity of thesample A, laser beams L radiated from the optical fiber tube isintroduced in the access port P in a state as radiated, that is a stateof not exerting severe influence on the windowpane or so, and the laserenergy is centered in the sample A by collecting the laser beams L atthe position sufficiently close to the sample A. The focusing againstthe sample A is simplified and the diameter of the beam spot alsobecomes smaller by disposing the condenser lenses 53 near by the sampleA in the cage 7 as mentioned above, therefore the effective heating canbe performed and the heat-resisting coating of the windowpane becomesunnecessary.

Furthermore, the electrostatic levitation furnace 1 has excellentfunctions in addition to the small-sized body as mentioned above, and itis suitable to be used in the space in which there is severe restrictionin size and weight. In the application in space, that is in thenon-gravity field, the electrostatic levitation furnace is to be used,which is equal to the aforementioned example substantially in the basicstructure, but changed in the supplying means and the collecting meansfor the sample A.

FIG. 9 is a drawing for explaining another example of the supplyingmeans of the sample A. The sample supplying means shown in FIG. 9 isinstalled with a cover 62 having an aperture 61 in the center thereof tothe upper end of a cylindrical casing 60, and provided with a solenoid63 forming an electromagnet, an iron core 65 disposed at the upper endof the solenoid 63, and a plunger 64 actuated by the solenoid 63 on theinside of the casing 60. The plunger 64 is provided with a chuck 67having a spring receiver 66 and a pair of holder pieces 67 a and 67 a atthe top end thereof, and a helical compression spring 68 is intervenedbetween the cover 62 and the spring receiver 55 in the casing 60.

The chuck 67 is composed by connecting the pair of holder pieces 67 aand 67 a rotatably with each other through a pin 69, and so structuredas to hold the sample A between holder pieces 67 a and 67 a protrudingupwardly from the aperture 61 of the cover 62. In this time, the pair ofholder pieces 67 a and 67 a is prevented to close by the sample A andenergized downwardly by the helical compression spring 68 as shown inFIG. 9(a), accordingly they are in a state of being energized in theclosing direction by contacting with an edge of the aperture 61, andhold the sample A in this state. The plunger 64 is situated in aposition where a gap in the vertical direction exists between thisplunger 64 and the iron core 65. The above-mentioned sample supplyingmeans can be equipped to the positive electrode EZ2 on the Z-axisinstead of the insulating holder 23.

In a case of releasing the sample A, the sample A is charged, forexample, by heating, and then attractive force is generated for thesample A by electrostatic field in the direction of an arrow as shown inFIG. 9. Next, by electrically charging the solenoid 63, the plunger 64is attracted toward the iron core 65 and goes up as shown in FIG. 9(b),whereby the holder pieces 67 a and 67 a are allowed to move in theopening direction by separating from the edge of the aperture 61, andstart to release the sample A at the same time.

The chuck 67 goes down together with the plunger 64 according to theelasticity of the helical compression spring 68 by interrupting theelectrical charge to the solenoid 63 successively to the start ofreleasing the sample A. In this time, the chuck 67 releases the sample Aat the same time of the closing action of the holder pieces 67 a and 67a as shown in FIGS. 9(c) and (d), and the chuck 67 is finally housed inthe casing 60 through the aperture 61 as shown in FIG. 9(e).

It is possible to release the sample A without rotation it by using theaforementioned sample supplying means. Namely, if the chuck of openingtype is used in the zero-gravity space, there is high possibility ofgiving rotation to the released sample according to uneven contact ofthe sample with the opening chuck since the contact between the sampleand the chuck on the whole is not always uniform, and it becomesdifficult to obtain uniform composition owing to centrifugal forcecaused by the rotation when the sample is rotated. Accordingly, in thiselectrostatic levitation furnace 1, the chuck 67 is so designed as torelease the sample A without rotation by actuating the one pair ofholder pieces 67 a and 67 a in the closing direction.

The released sample A is maintained in the levitation state between theelectrodes disposed on the three axes similarly to the previouslymentioned example, and subjected to heating by laser beams. In thistime, since the three pairs of electrodes EZ1, EZ2, EX1, EX2, EY1and EY2which are equivalent in their generative electrostatic fields areadopted in this electrostatic levitation furnace 1, the controllingforces in the directions of three axes caused by the respectiveelectrodes become uniform and the sample A is securely maintained in thelevitation state in the zero-gravity space.

FIG. 10 is a drawing for explaining another example of the collectingmeans for the sample A. The sample collecting means shown in FIG. 10 isattached with a lid 71 to one side of the upper part of a case 70 madeof heat-resisting glass so as to swing freely, and disposed detachablywith a reflector plate 72 made of heat-resisting resin on the under faceof the lid 71. The case 70 is disposed with a buffer plate 73 made ofheat-resisting resin on the bottom thereof, and provided protrudinglywith a stopper 74 to be in contact with the top end of the lid 71 at theother side of the upper part of a case 70. Further, the lid 71 is formedwith an opening 75 from the base end to the top end thereof, anddisposed with a pusher bar 76 correspondingly to this opening 75 so asto move in parallel with the upper edge thereof.

In the aforementioned sample collecting means, the sample A finishedwith the heating process is pressed by the manipulator or the like, andcontained into the case 70 after striking against the reflector plate 72as shown in FIG. 10(a). After this, when the pusher bar 76 is movedforwardly with another manipulator or the like as shown in FIG. 10(b),the pusher bar 76 comes in contact with the reflector plate 72 throughthe opening 75, thereby swinging the lid 71 in the closing directiontogether with the reflector plate 72.

In the process of travel of the pusher bar 76 to the forward limit, thereflector plate 72 is removed from the lid 71 by the pusher bar 76continuously going forward after the lid 71 is restricted to swing bythe stopper 74, and the reflector plate 72 closes up the upper side ofthe case 70 tightly as shown in FIG. 10(c). After this, when the insideof the vacuum chamber 3 is recovered into the predetermined atmosphericpressure, the reflector plate 72 shifts into the bottom side accordingto the difference between internal and eternal pressure of the case 70as shown in FIG. 10(d), so that the sample is held between the reflectorplate 72 and the buffer plate 73.

Although it is impossible to successively supply and collect the sampleA by the sample supplying means and the sample collecting means asdescribed in this example, the electrostatic levitation furnace 1 isprovided with the detachable cage 7 in the vacuum chamber 3, and it ispossible to easily supply and collect the new sample A comparatively bydisposing the respective means so as to be detachable from the cage 7.

In addition to the above, although the furnace 1 is structured so thatthe sample A is charged by heating with laser beams irradiated from theopening 19 of the negative electrode EZ1 on the Z-axis and molten byheating with laser beams irradiated from the laser irradiators Q1 to Q4disposed in the four points in the aforementioned respective examples,it is also possible to integrate one of four laser irradiators Q1 to Q4with the negative electrode EZ1 and use this laser irradiator both forelectrification and melting. Adopting such the construction, the spacearea can be saved by the integration of the laser irradiators,consequently the degree of freedom is further improved in distributionof the other electrodes, the laser irradiators or the other apparatuses.

FIG. 11 and FIG. 12 are drawings for explaining another example of theelectrostatic levitation furnace according to this invention. Theelectrostatic levitation furnace in this example is provided withelectrodes EZ1 and EZ2 opposed to each other on the vertical axis(Z-axis) in the gravitational field, and equipped with an opening 19 afor irradiating laser beams to the positive electrode EZ2 on the lowerside.

The positive electrode EZ2 is formed by plating a material made of toughpitch copper with gold and subjected to mirror finish, the top end faceF of the electrode EZ2 is formed in a nearly hemispherical concaveshape, and formed with the opening 19 a in the center thereof. Thepositive electrode EZ2 is further provided with a net-like shapedholding means 80 made of tungsten as a means for placing the sample A,and so designed as to hold the sample A in a state separated from thetop end face F by this holding means 80 as shown in FIG. 12.

The above-mentioned positive electrode EZ2 is secured to a hollowelectrode base 81 opened in the vertical direction. The electrode base81 is connected with a hollow-shaped lens holder 82 opened in thevertical and lateral directions. The lens holder 82 maintains acondenser lens 83 together with the electrode base 81 and maintains areflector 86 in an inclined state by a mirror presser 84 and a holderblock 85 fixed on the lower side thereof. Further, the holder block 85is provided with a power-leading terminal 87, and this power-leadingterminal 87 is connected to the positive electrode EZ2 through a leadwire 88 and so on.

On the other side, the negative electrode EZ1 on the upper side hassimilarly an opening 19 b at the center, and secured to a hollowelectrode base 89. This electrode base 89 is connected to a lens holder90 opened in the vertical and lateral directions. Furthermore, areflector 93 is maintained to the lens holder 90 in an inclined state bya mirror presser 91 and a holder block 92 fixed on the upper side of thelens holder 90.

The aforementioned positive electrode EZ2 and negative electrode EZ1 areused for the upper and lower electrodes opposed with each other on thevertical axis in the electrostatic levitation furnace as mentioned inthe previous example, in this case these electrodes are disposed so thata lateral opening 82 a of the lens holder 82 of the positive electrodeEZ2 may be opposed to a laser emitter 94 or an optical path from thelaser emitter 94, and a lateral opening 90 a of the lens holder 90 ofthe negative electrode EZ1 may be opposed to a laser damper 95 or anoptical path extending to the laser damper 95.

In the electrostatic levitation furnace having the aforementionedconstruction, laser beams L radiated from the laser emitter 94 isintroduced into the lateral opening 82 a of the positive electrode EZ2,and this laser beams L is collected by the condenser lens 83 after beingreflected in the upward direction by the reflector 86, whereby thesample A is irradiated with laser beams L from the under side thereof.In a case where the sample A moves laterally and deviates from laserbeams L at the time of making the sample A in the levitation state,laser beams L is introduced into the negative electrode EZ1, andreflected toward the laser damper 95 through the reflector 93.

The above-mentioned electrostatic levitation furnace is suitable forperforming heating process in the gravitational force to the sample Acontaining high-melting point metal as the main components, for example.In order to carry out this heating process, the sample A is placed onthe holding means 80 as shown in FIG. 12 and heated up to a temperaturelower than the melting point (for example, 1200° C. or so) byirradiating laser beams L from the lower side, thereby removinglow-melting elements contained in the sample A (baking).

In this electrostatic levitation furnace, since the top end face F ofthe positive electrode EZ2 is formed in the hemi-spherically concaveshape, the radiant heat is transferred efficiently to the sample A bythe top end face F (concave shape), whereby heating efficiency isimproved and the sample A can be heated up to the desired temperature ina short time. Further, the holding means 80 is able to hinder securelyan accident such that the molten sample A sticks to the surface of thepositive electrode EZ2, thereby preventing the positive electrode EZ2from the stain and the thermal injury of the electrode face.

Furthermore, in a case of heating the sample A in this manner, it ispossible to make the sample A hard to stick to the holding means 80 byradiating laser beams L in a pulse mode and heating the sample Astrikingly by this pulsed laser beams L. The sample A is similarlyenabled to be hard to stick to the positive electrode EZ2 even when theholding means 80 is not provided.

Subsequently, in the electrostatic levitation furnace, the sample A ismade into the levitation state between the electrodes EZ1 and EZ2 (EX1and EX2, EY1 and EY2) after properly cooling it, and then the sample Ais molten by heating with laser beams L irradiated from a single orplurality of the laser irradiator(s).

In this electrostatic levitation furnace, it is possible to carry outthe heating (baking) and the melting of the sample A successively andpossible to reduce time required for melting the sample A after makingit in the levitation state by disposing the negative electrode EZ1 andthe positive electrode EZ2 at the upper and the lower positions on thevertical axis and irradiating laser beams to the sample A from thepositive electrode EZ2 on the lower side as mentioned above. Concretely,it takes 5 minutes or more to melt the sample A in conventional art, butit is possible to melt the sample A for several seconds to several tensof seconds, and possible to reduce time required for melting remarkablyin this electrostatic levitation furnace.

Moreover, in this electrostatic levitation furnace, pressure of laseracts in the direction in which the gravity is cancelled in the case ofmaking the sample A into the levitation state, and it is possible toreduce an electrostatic force required for levitation, in other wordspossible to make the heavier sample A in the levitation state by thesame electrostatic force. Further, although the spherical sample isgenerally used in the conventional furnace, it is also possible to usethe sample other than in spherical shape in this electrostaticlevitation furnace since the electrification of the sample A ismaintained effectively. Accordingly, the sample A becomes unnecessary tobe form in the spherical shape. Additionally, the moment when the sampleA gets to melt can be judged visually and very easily because the samplein any shape excepting the spherical one changes into spherical shape atthe time of the melting.

Although the construction in which the laser irradiator is incorporatedto the positive electrode EZ2 on the lower side is explained in thisexample, it is also possible to dispose these apparatuses separately andirradiating laser beams from the under side of the sample A. In thiscase, laser beams may be irradiated from the position directly ordiagonally below the sample A, further may be irradiated from aplurality of positions. When laser beams are irradiated to the sample Afrom, for example, the three points on the diagonally under side, thesample A is heated similarly in the case of irradiating laser beams fromthe just under side of the sample A. In such the manner, it is possibleto similar effects to the aforementioned example even in the case ofseparating the laser irradiator from the electrode.

Industrial Applicability

According to this invention, in the electrostatic levitation furnace formaking the sample into the levitation state between the electrodes, theaccessible direction for the sample A, such as the heating of thesample, the position detection, the temperature measurement, theillumination, the photographing and the like becomes multiple, inaddition to the generation of the electrostatic field from threedirections for the sample A, accordingly it is possible to improve thedegree of freedom of the distribution of various apparatuses in spite ofthe small body and further possible to deal with the increase of theapparatuses as compared with the conventional case of accessing thesample on the same plane.

Further, the interference between the electrodes and the variousapparatuses can be easily avoided according to the multiplication of theaccessible direction for the sample, so that it is possible to use threepairs of electrodes equivalent in their electrostatic field intensityfor the purpose of making the controlling forces uniform, and possibleto properly dispose the plural laser irradiators for the purpose ofimproving the heating performance. Furthermore, it is possible to obtainthe sufficient vacuum atmosphere even by the small-sized vacuum systemaccording to miniaturization of the vacuum chamber, and it is easy tointroduce the manipulator or the like for performing proper operationagainst the sample between electrodes because of short distance from thesample. According to these advantages, it is very suitably used in thespacecraft in which there is severe restriction in size and weight.

In the preferred embodiment of the electrostatic levitation furnaceaccording to this invention, which is adopted with three pairs ofelectrodes equivalent in their electrostatic field intensity, it ispossible to make the controlling forces uniform between the respectiveelectrodes, the sample can be securely maintained in the levitationstate at the predetermined position, thereby enabling the heatingprocess satisfactory.

In another preferred embodiment of the electrostatic levitation furnaceaccording to this invention, it is possible to very easily change theelectrodes according to size of the sample or so by preparing the pluralcages provided with the electrodes differing in size or distance of themin advance. Further, the cage can be attached with apparatuses otherthan the electrode, and it is possible to easily set parts to bedisposed in the vicinity of the sample such as a condenser lens of laserbeams or the like.

In the other preferred embodiment of the electrostatic levitationfurnace according to this invention, in which the electrodes aredetachable from the cage, it is possible to very easily change theelectrodes according to size of the sample or so by using the singularcage.

Further, in the other preferred embodiment of the electrostaticlevitation furnace according to this invention, in which the cage isdisposed with the power terminals, the cage becomes more suitable to bedispose with the electrodes and the apparatuses required for powersupply, and it is also possible to easily carry out the wiring work andso.

Furthermore, in the other preferred embodiment of the electrostaticlevitation furnace according to this invention, it is possible to heatthe sample uniformly and possible to form more satisfactory crystalbecause the laser irradiators to heat the sample are disposed at pointscorresponding to the respective apexes of the triangular pyramid havingthe center at the position where the sample is to be levitated.

In the other preferred embodiment of the electrostatic levitationfurnace according to this invention, in which the laser irradiator isequipped to one of electrodes, it is possible to successively carry outthe electrification of the sample and the levitation of the samplebetween electrodes by heating with laser beams in the case of subjectingthe sample to the heating process especially in the gravity. Further, itis also possible to incorporate one of laser irradiators disposed to therespective apexes of the triangular pyramid to the electrode, in thiscase, the space area can be saved according to the incorporation and itis further increase the degree of freedom in distribution of the otherelectrodes, the laser irradiators or the other apparatuses.

Moreover, in the other preferred embodiment of the electrostaticlevitation furnace according to this invention, the sample can bereleased between the electrodes without rotation in a case of being usedespecially in the non-gravitational field, and it is possible tocontribute to the satisfactory crystallization by subjecting the sampleto the heating process or the like without receiving influence of thecentrifugal force.

Furthermore, in the other preferred embodiment of the electrostaticlevitation furnace according to this invention, since the heating isdone by irradiating laser beams from the under side of the sample, themolten sample becomes difficult to stick on the electrode surface andthe electrode face can be prevented from the stain and the thermalinjury. Further, because the laser pressure acts in the direction inwhich the gravity is cancelled and the electrification of the sample ismaintained effectively in the case of making the sample into thelevitation state, it is possible to reduce the electrostatic force orincrease the sample weight and the sample in a shape other thanspherical is enabled to be used. In the case of using the sample in suchthe shape, the sample changes into spherical shape at the same time ofmelting, therefore it is possible to visually and very easily judge themoment when the sample A gets to melt. Additionally, it is possible toreduce time required for melting the sample after making it in thelevitation state by heating the sample in the levitation state after theheating (baking) in addition to the laser irradiation from the underside.

In the other preferred embodiment of the electrostatic levitationfurnace according to this invention, the top end face of the electrodeis formed in the hemi-spherically concave shape, therefore the radiantheat can be transferred efficiently to the sample and it is realizeimprovement of the heating efficiency and the further reduction of themelting time.

Furthermore, in the other preferred embodiment of the electrostaticlevitation furnace according to this invention, it is possible tosecurely hinder the accident such as sticking of the molten sample onthe electrode surface and possible to improve the preventing function ofthe stain and the thermal injury of the electrode surface by the holdingmeans disposed to the lower side electrode.

1. An electrostatic levitation furnace for generating electrostaticfield between electrodes disposed in a vacuum chamber and making acharged sample into a levitation state in the electrostatic fieldbetween the electrodes, said furnace comprising: three pairs ofelectrodes opposed to each other respectively on three axesperpendicularly intercepting each other at a position where the sampleis to be levitated in the vacuum chamber; and a plurality of accessports disposed tree-dimensionally to said vacuum chamber and directed tothe position of said levitating sample.
 2. An electrostatic levitationfurnace as set forth in claim 1, wherein said three pairs of electrodesare equivalent in their electrostatic field intensity.
 3. Anelectrostatic levitation furnace as set forth in claim 1, wherein saidvacuum chamber is detachably disposed with a cage therein, and saidrespective electrodes are provided to the cage.
 4. An electrostaticlevitation furnace as set forth in claim 3, wherein said respectiveelectrodes are detachable from the cage.
 5. An electrostatic levitationfurnace as set forth in claim 3 4, wherein said cage is provided with apower terminal.
 6. An electrostatic levitation furnace as set forth inclaim 1, wherein said furnace is provided with laser irradiatorsdisposed at respective points corresponding to apexes of a triangularpyramid of which center coincides with the position of said levitatingsample for irradiating laser beams against the sample.
 7. Anelectrostatic levitation furnace as set forth in claim 1, wherein saidfurnace is provided with a laser irradiator disposed to one of saidelectrodes for irradiating laser beams against the sample.
 8. Anelectrostatic levitation furnace as set forth in claim 1, wherein saidfurnace is provided with a chuck for holding the sample to be releasedbetween the electrodes, and said chuck is provided with a pair of holderpieces energized in a closing direction for pinching the sampletherebetween.
 9. An electrostatic levitation furnace as set forth inclaim 7, wherein said laser irradiator is disposed to the electrode onlower side between vertically opposed electrodes in a gravitationalfield.
 10. An electrostatic levitation furnace as set forth in claim 9,wherein said lower electrode is provided with a concave face havingnearly hemispherical shape at a top end face thereof.
 11. Anelectrostatic levitation furnace as set forth in claim 9, wherein saidlower electrode is provided with a holding means having net-like shapefor placing the sample thereon.